Daily nutrient utilization and swimming activity patterns in Senegalese sole (Solea senegalensis) post-larvae

Numerous metabolic and physiological processes are rhythmically regulated in order to accomplish the animal energetic daily demands. The precise knowledge of how metabolic fluxes are modulated is essential to adjust the dietary formulation to satisfy fish energetic demands. In the present study, nutrient (lipid and protein) metabolism and swimming activity were assessed, during a complete daily cycle in Senegalese sole post-larvae (63 days post-hatching), using tube-feeding technique and video-recording approaches. Lipid absorption and retention efficiency were higher in post-larvae fed during the night than those fed during the day. Protein metabolism was not affected by daily cycle. Regarding the swimming activity, a period of higher swimming activity was recorded at 04:00 and at 12:00 h followed by a basal activity of approximately 20% during the rest of the day. Results suggest that post-larvae present higher lipid absorption and retention capacities during the night. The higher swimming activity observed from the mid of the night period until early hours was most likely sustained by a higher feed intake. In conclusion, these results provide useful insight in how fish modulates metabolism to accommodate physiological needs in relation to energy reserves. Sole post-larvae presents a low capacity to digest dietary lipid during daytime. In the future these findings may be used to improve dietary formulations and increase sole growth performance.This work received national funds through FCT- Foundation for Science and Technology through project CCMAR/Multi/04326/2013 (Portugal), project SOLEAWIN (310305/FEP/71) partially supported by PROMAR Program (Portugal) with FEDER funds, and also through the Spanish Ministry of Economic Affairs and Competitiveness (MINECO) by projects RIDIGEST (AGL2011-23722) and EFISHDIGEST (AGL2014-52888-R) with FEDER/ERDF contribution granted to M. Yúfera (Spain). Carmen Navarro-Guillén was supported by a doctoral fellowship (BES-2012-051956) from MINECO (Spain). Sofia Engrola acknowledges a FCT investigator grant IF/00482/2014/CP1217/CT0005 funded by the European Social Fund, the Operational Programme Human Potential and the Foundation for Science and Technology of Portugal (FCT – Portugal).Peer reviewe